Meter reading systems, such as automatic meter reading systems (AMR) and advanced meter infrastructure (AMI) systems, are generally known in the art. Utility companies uses such meter reading systems to read and monitor customer utility meters remotely, typically using radio frequency (RF) communication. AMR and AMI systems increase the efficiency and accuracy of collecting readings and managing customer billing.
Utility meters are often denoted smart meters and provided with communication devices for transmitting and receiving RF signal. The communication devices may be configured to periodically transmit data packets including data representing multiple meter readings and other meter data as a function of time.
Good precision, long-term stability, low power consumption and robustness makes utility meters based on ultrasonic time-of-flight technology a widespread choice for monitoring consumption of potable water, hot water, water-based heating and cooling power etc. However, as most ultrasonic flowmeters are battery-powered, strict power management must be enforced in order to keep the average meter power consumption at a minimum. Typical values hereof are between 5 and 50 microamperes supplied from a 3.6 V lithium battery. Another important design criterion for flowmeter devices is the precision of the flow determination.
In a time-of-flight ultrasonic flowmeter the flowrate is determined by clocking the difference in transit times of counter- and co propagating ultrasonic signals. Here, the transit time is considered to be the time an ultrasonic wave front takes to traverse the fluid from transmitting transducer to the receiving transducer. A measure for the transit time is the phase difference, Δϕ between two oscillations making up the wave packets. However, determining the flow rate based on phase difference is complicated by the fact that the speed of sound, which is part of the flow rate calculations, is temperature dependent. Consequently, in order to perform an accurate measurement of the flowrate, not only must the phase difference be measured, but also the speed of sound, must be inferred. However, inferring the speed of sound may require substantial data processing, which increases power consumption.
Hence, an improved flowmeter with reduced average meter power consumption would be advantageous, and in particular a flowmeter with reduced data processing and good precision would be advantageous.